1. Field of the Invention
This invention relates to the preparation of ureas, and, more particularly, is concerned with a novel process for the preparation of cyclic alkylene ureas and novel intermediates therefor.
2. Description of the Prior Art
The preparation of cyclic alkylene ureas is well known in the art and a number of different procedures have been described. Illustratively, alkylene diamines can be reacted with carbon dioxide to form the corresponding alkylene urea but high temperatures and pressures are required; see Ind. Eng. Chem. 1948, 40, 393. In a more classic reaction, phosgene is reacted with an alkylene diamine to form the urea (see Annalen, 1937, 532, 300) but the disadvantage in this procedure is the commercially unacceptable high weight loss arising from the two chlorine atoms in addition to low product yield due to losses from polymer forming side reactions.
Other routes to cyclic ureas have been found but these require a number of cost increasing or cumbersome steps to reach the product. For example, lactam oximes can be rearranged to cyclic ureas by polyphosphoric acid as noted by Behringer et al (Annalen, 1957, 607, 67); LeBerre et al (Bull Soc. Chim. 9, 3245, 1971) have found that the p-toluenesulfonate ester derivative of a lactam oxime can be rearranged to the urea by treatment with base.
The preparation of cyclic alkylene thioureas has been described, see Organic Syntheses 26, 34, or Arya et al, Indian Journal of Chemistry, 14B, p. 773, 1976. However, the conversion of the thiourea to the corresponding urea requires an expensive oxidation step.
Unexpectedly, we have found that certain species of cyclic alkylene ureas can be prepared via a novel process which overcomes both of the prior art problems of multi-step syntheses and expensive oxidation steps. Moreover, our novel process provides an additional benefit in terms of both unit processing and unit operation because the whole process can be carried out in the same reaction vessel without the need for the isolation of intermediates.